Balanced radio frequency circuit



Dec. 3, 1940. c. w. HANSELL EI'AL 2,223,416

BALANCED RADIO FREQUENCY CIRCUIT Filed Feb. 25, 1938 INPUT 1 C D 42 INVENTORS C- W. HANSELL BY H. E. STINE Patented Dec. 3, 1940 UNITE STATES azzaiit 2,223,416 BALANCED RADIO FREQUENCY CIRCUIT Application February 23, 1938, Serial No. 191,854

2 Claims.

This application concerns a new and improved method of and means for balancing radio frequency circuits.

In radio frequency circuits, especially those 5 operating at the higher frequencies, it is essential that the input circuits be balanced to ground as nearly as possible and that the output or anode circuits also be balanced with respect to ground, the tube apparatus, etc. In order to obl tain this symmetry and balance in practice it is essential that there be mechanical symmetry of the circuits as well'as electrical symmetry. In a circuit where it is desirable to use a single tube, for example, in a radio frequency oscillator 15 or a radio frequency amplifier circuit, the problem of mechanical and electrical symmetry becomes more difficult.

An object of this invention is to provide a new and improved balanced circuit arrangement 0 applicable to a single stage or to a double stage and also applicable to a single stage between double stages or between a double stage and a single stage.

In describing my invention more in detail, reference will be made to the attached drawing,

wherein Figure 1 illustrates diagrammatically the essential features of a radio frequency circuit arranged in accordance with my invention; while 30 Figure 2 illustrates a modification of the arrangement of Figure l which is in principle a circuit substantially the same as the circuit of Figure 1. In Figure 2, however, a particular type of structure including neutralizing con- 35 densers and tube supporting apparatus, is shown.

Referring to Figure 1 of the drawing an electron discharge device It has its control grid connected with a radio frequency input circuit I2 and its anode connected with a radio fre- 40 quency output circuit 14. If the stage is to act as a relay or amplifier wave energy is impressed from 5 on l2 and from M on l3. Wave energy, however, may be generated in. the tube and circuits by proper adjustment and operation there- 45 of. The anode 9 of tube it is connected as shown by way of a neutralizing condenser C2 to a point on the inductance of circuit l2. The capacity of this condenser which is preferably variable, is approximately equal to the grid to plate capacity of tube Ill. The control grid 1 is also'connected to a point on the inductance of output circuit M by a variable condenser C3 which may also be considered an additional neutralizing or balancing condenser. These two points at which 55 0'2 and CE; are connected on the inductance of l2 and M, respectively, are coupled together by an additional condenser G1, which, if we look at this relaying system as a balanced push-pull stage, may have a capacity of the order of the capacity between the grid 1 and anode 9 of 5 tube Ill. The purpose of the capacity C3 is to balance the voltagethat is impressed across C1. C4 is an additional small preferably variable condenser having a value of the order of the capacity between the grid 1 of tube 9 and the 10 cathode 5 or ground. In other words, the arrangement at C1 and C4 simulates an additional tube in this circuit so that although a single stage is used the circuits are neutralized and balanced in both directions.

An embodiment which is preferred at the present time, is illustrated in Figure 2. Here the input circuit I2 and output circuit It are substantially as in the prior figure except for the coupling condensers CD in the input circult. The tube Hi, however, is included in a conical block not shown,'and mounted in an additional water-cooled block 20. The neutralizing condensers C2 and C3 are likewise for purposes of symmetry mounted in the blocks 2t and M, respectively. The condenser G1 which simulates the grid to plate capacity of tube It or an additional tube is also located as shown in the block 2|. The condensers C1, C2, and C3 may be of the compressed air neutralizing condenser type. The anode circuit 14 as illustrated in Figure 2 comprises fluid conductors as well as electrical conductors and by the means of these conductors cooling fluid is supplied to the blocks 20 and 2!. The conductors 22 are supplied with fluid at 26 which, after circulation in the system, returns to its source at 26.

By using equal size blocks on both sides of the circuit the block capacity to ground of both sides or the grid and plate circuits are balanced and this when taken with the neutralizing arrangement including condensers C2 and C3 insures a completely balanced circuit. The balancing condenser C1 shown in Figures 1 and 2 may not in some cases be necessary to form a suiiiciently balanced circuit. This condenser may also be eliminated and its capacitive effect be obtained by making one of the grid leads have a larger capacity to ground than the other, thus affording the necessary capacity balance without adding a condenser to the circuit. By this is meant that the lead to which the upper terminal of C4 is connected may be made larger, this being in the position of the grid lead in case this circuit is looked at as a push-pull balance circuit.

An outstanding advantage of the circuit of the present invention as illustrated in Figures 1 and 2 is that it is Very well adapted to use in transmitters Where some stages have one tube and some stages have two tubes. Moreover, while the invention is shown as being applied to a single tube circuit it is within the scope of this invention to use more than one tube, in which case the additional tube would replace the condenser C1 in Figures 1 and 2. Moreover, I contemplate the use of more than one tube in each side of the circuit, that is, the use of tubes in parallel and by selecting the proper size of balancing condensers, obtaining the same balanced symmetry of a single tube. The invention is applicable to oscillator circuits, in which case condensers C2 and C3 would be used to control the regeneration of the feedback voltage rather than as neutralizing condensers.

The nature of the neutralizing condensers of the compressed air type and the water-cooled blocks and circuits of Figure 2 have been set forth more in detail and claimed in my United States application Serial #93393 filed July 30, 1936 U. S. Patent 2,146,541, issued Feb. 7, 1939.

1. A single tube balanced high frequency circuit comprising a symmetrical alternating current input circuit, a symmetrical resonant loop output circuit, a metallic block connected to each end of said loop, an electron discharge device having a control electrode, a cathode and an anode, said anode being connected to one of said blocks, a neutralizing condenser mounted on said one block and having an electrode connected thereto, a pair of condensers mounted on the other of said blocks and each having an electrode connected thereto, a connection from said control electrode to a condenser on said other block, a connection between the remaining condenser on said other block and a condenser on said first block and an additional capacity between said last named connection and a point of electrical symmetry of the order of the control electrode-cathode capacity of said tube.

2. A singl tube balanced high frequency circuit comprising a symmetrical alternating current input circuit, a symmetrical resonant loop output circuit, a metallic block connected to each end of said loop, an electron discharge device having a control electrode, a cathode and an anode, said anode being connected to one of said blocks, a neutralizing condenser mounted on said one block and having an electrode connected' thereto, a pair of condensers mounted on the other of said blocks and each having an electrode connected thereto, a connection from said control electrode to a condenser on said other block, a connection between the remaining condenser on said other block and the condenser on said first block, the capacity of said remaining condenser being of the order of the control electrode-anode capacity of said electron discharge device and an additional capacity between the last named connection and a point of electrical symmetry of the order of the control electrodecathode capacity of said electron discharge de- Vice.

CLARENCE W. HANSELL. HALLAN E. GOLDSTINE. 

